Earth and Planetary Astrophysics
Exoplanet Orbital Distribution around FGK Sun-like Host Stars II: a valley in the orbital semi-major axis distribution of sub-Neptunes
Li Zeng, Stephanie C. Werner, Stein B. Jacobsen et al. (+3 more)
More than one hundred years ago, physics has been revolutionized when people realized that electronic orbitals, or electromagnetic interactions in general, are quantized. Now, in this study, we are presenting evidence of quantization of
planet orbits around
stars. Confining a wave in spatial dimensions "quantizes" its wave number. Therefore, this study points to the evidence of the existence of long-range standing waves in the proto-planetary disks. Such waves, although being on a much larger scale of few tens of AU, have already been found by ALMA observation-so called ring-like structure. Now we see that it may exist within 1 AU, and may exert its effect on the existence and distribution of
planets within this distance range to the host
star. Careful analysis has been carried out to compare the results of different surveys.
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All authors Li Zeng, Stephanie C. Werner, Stein B. Jacobsen, Elena Mamonova, Reidar G. Trønnes, Ramon Brasser
Astrophysics of Galaxies
Expansion kinematics of young clusters. III. The kiloparsec sample
Joseph J. Armstrong and Jonathan C. Tan
We combine
Gaia DR3 5-parameter astrometry with calibrated radial velocities for 23 nearby (<1 kpc) young (<60 Myr) clusters, with membership lists from Cantat-Gaudin et al. (2020). We characterise the plane-of-sky structure of the clusters using Q-Parameter and Angular Dispersion Parameter (ADP) methods. We measure plane-of-sky expansion using several methods. We determine plane-of-sky orientations along which expansion is maximised. We also estimate expansion timescales and traceback ages and compare to isochronal ages. We then look for correlations between cluster properties and discuss sample-wide trends. We find that most young clusters are more smoothly structured in their centers where the rate of dynamical interactions is highest, while hierarchical structure can survive in the sparse outskirts for >10 Myr. We also find that the majority of nearby young clusters exhibit clear signatures of expansion in the plane-of-sky, which in many cases is significantly anisotropic, even at ages >30 Myr. We find evidence that older clusters tend to have directions of maximum expansion oriented closer to parallel with the
Galactic plane. The high degree of spatial structure and significant expansion anisotropy imply that the majority of these young clusters have formed with significant spatial and kinematic substructure and not as dense, monolithic clusters. Kinematic ages estimated from expansion timescales and on-sky traceback are generally in good agreement with estimates inferred from
stellar evolution models for clusters <10 Myr old. However, many clusters with older isochronal ages appear to have significantly younger kinematic ages. We discuss potential reasons for this discrepancy, including a prolonged embedded and/or gravitationally bound phase in the early stages of the clusters.
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Astrophysics of Galaxies
Morphological complexity of NGC 628 - a multiwavelength multiscale analysis using the ordinal pattern framework
Athokpam Langlen Chanu, S Amrutha, Pravabati Chingangbam et al. (+1 more)
As statistical systems,
galaxies exhibit a rich interplay between organized structure and
stochastic fluctuations across a broad range of spatial scales. This duality motivates the need for quantitative frameworks capable of capturing their morphological complexity. The ordinal patterns framework, along with its associated statistical measures: permutation
entropy ($H$), disequilibrium ($D_E$), statistical complexity ($C$), and ordinal network node
entropy, has recently emerged as a powerful tool for analyzing such complexity in physical systems. We apply this framework in a multiwavelength, multiscale analysis of the
galaxy NGC 628, utilizing observations in the near-ultraviolet, near-infrared, mid-infrared, and millimeter bands. Our results reveal a characteristic spatial scale of approximately 200 parsecs, marking the transition from small-scale structures influenced by
star formation and
stellar feedback to larger-scale morphology governed by the
galaxy's dynamics. Furthermore, we find that the $C$ vs. $H$ trajectories for all wavelengths converge toward a common attractor curve, consistent with the behavior of isotropic Gaussian random fields. This convergence suggests a universal statistical behavior in
galactic structure at large scales, despite the differing physical processes traced by each wavelength.
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All authors Athokpam Langlen Chanu, S Amrutha, Pravabati Chingangbam, Changbom Park
Earth and Planetary Astrophysics
Exoplanet Orbital Distribution around FGK Sun-like Host Stars I: planet occurrence rate derived from the Kepler Mission and theoretical interpretations from planet formation
Li Zeng, Stephanie C. Werner, Stein B. Jacobsen et al. (+3 more)
Recent astronomical observations, in particular from the Kepler and TESS missions and their related follow-ups, have revealed an abundance of
exoplanets in the size range between Neptune (4 Earth radii) and Earth (1 Earth radii ), as well as a low occurrence rate of
planets around twice the radius of Earth (2 Earth radii). This paper uses statistical methods, in particular, the survival function analysis, to address the known
exoplanet population observed mainly from the Kepler's primary mission, in order to mathematically elucidate the orbital distributions (expressed in either the orbital period P or the orbital semi-major axis a), for each of the host
stars, in both a collective way, and also separately for the
planets grouped into various radius bins. We uncover a log-uniform distribution for the majority of
planets except the
giants. Based on the results of the statistics, we then visit several possible formation scenarios and pathways for
planets in different size ranges, in order to explain the results from a theoretical point-of-view.
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All authors Li Zeng, Stephanie C. Werner, Stein B. Jacobsen, Elena Mamonova, Reidar G. Trønnes, Ramon Brasser
Astrophysics of Galaxies
Neutral Hydrogen in the Shapley Supercluster Core I: Environmental Effects on Gas Content and Galaxy Evolution
L. Gwebushe, T. Venturi, P. Merluzzi et al. (+5 more)
We study the atomic Hydrogen (HI) content of
galaxies in the core of the Shapley Supercluster (SSC) at <z> ~ 0.048, using observations from the MeerKAT
Galaxy Cluster Legacy Survey and optical data from the Shapley Supercluster Survey (ShaSS) project. Our sample comprises 169
galaxies with HI detections in the dynamically active region of Abell 3558 and SC1329-313. Following the literature, we classify
galaxies into
star-forming main sequence (SFMS), transition (TZ), and red sequence (RS) populations, and examine how the HI content varies across these populations.
Galaxies on the SFMS exhibit an average HI gas fraction offset of 0.038 dex from the gas fraction main sequence, while TZ and RS populations show depleted HI fractions of -0.034 and -0.211 dex. HI depletion timescales span from 6 to 170 Gyr (SFMS-TZ-RS) confirming increasingly inefficient
star formation with quenching. Scaling relations between HI mass and
stellar mass in the SSC are generally consistent with field samples. The most direct signature of the dense environment of the SSC is the marked predominance of TZ
galaxies, in contrast to what is observed in the field-dominated sample of xGASS, where the population is mostly composed of SFMS
galaxies. Moreover, the SFMS and RS populations have similar size, again in contrast with field populations. These results suggest that
galaxies in the SSC are undergoing environmental quenching through starvation or strangulation, rather than rapid gas stripping. Despite detectable HI reservoirs, many
galaxies exhibit long depletion times, indicating reduced gas
accretion and inefficient
star formation.
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All authors L. Gwebushe, T. Venturi, P. Merluzzi, G. Busarello, V. Casasola, O. Smirnov, M. Ramatsoku, J. Dawson
Cosmology and Nongalactic Astrophysics
Ray-traced weak lensing convergence in screened modified gravity theories
Mattia Pantiri, Matthieu Schaller, Alessandra Silvestri et al. (+2 more)
Weak gravitational
lensing is one of the primary cosmological probes, providing powerful constraints on the cosmological model. As Stage IV surveys are expected to deliver data of unprecedented precision, accurate modeling of weak gravitational
lensing observables across both linear and non-linear scales becomes increasingly important. In this work, we investigate weak
lensing in modified
gravity (MG) models, extensions of the standard $\Lambda$CDM cosmology in which
gravity deviates from general relativity, generally introducing modifications to the
lensing equation. We parametrize these modifications through the common phenomenological function $\Sigma_\mathrm{mg}$ and apply ray-tracing to the density maps of N-body and hydrodynamical simulations. We model the time dependence of $\Sigma_\mathrm{mg}$ analytically, while we introduce a phenomenological scale dependence to represent the screening mechanisms by which MG models reduce to general relativity in high-density environments. Starting from the output of the FLAMINGO hydrodynamical simulations, we generate fully ray-traced convergence maps using our modified
lensing model. We analyze how the parameters of our prescription affect the weak
lensing convergence power spectrum and compare these effects to other known sources of variation, in particular cosmological parameters and baryonic feedback. We find that the modifications to the
lensing equation deriving from the MG model produce non-negligible signatures in the convergence power spectrum and that, within extensions of the $\Lambda$CDM framework, these effects can be larger than those induced by baryonic physics. Our results indicate that modified
lensing should become a standard ingredient of the analysis of modified
gravity simulations.
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All authors Mattia Pantiri, Matthieu Schaller, Alessandra Silvestri, Jeger C. Broxterman, Joop Schaye
Solar and Stellar Astrophysics
Searching for Ultracool Dwarfs in Early LSST Data Products
Easton J. Honaker, John E. Gizis, Christian Aganze et al. (+8 more)
The Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) promises to drastically accelerate the discovery of ultracool
dwarfs (UCDs) over the course of its 10-year survey of the Southern Hemisphere. With the official start of LSST imminent, we showcase LSST's capabilities for discovering and characterizing UCDs using early commissioning data (Data Preview 1). The LSST photometric system at this stage remains poorly understood for faint UCDs. Thus, we begin by cross-matching Data Preview 1 against known UCD catalogs. We recover 1 known UCD from the Ultracool Sheet, 17 UCDs from the Dark Energy Survey, and 17 low mass
stars from the
Gaia Catalog of Nearby
Stars. Using these known UCDs alongside recent spectroscopically-confirmed Euclid objects, we select 89 ultracool
dwarf candidates in LSST fields, 17 of which are unique to this work. We present our candidates, a photometric temperature estimate, and discuss lessons learned from using early LSST data products. Finally, we turn to the future and predict potential UCD counts in upcoming LSST commissioning data (Data Preview 2), which is expected to be available to the Rubin community in 2026. Using synthetic populations of brown
dwarfs, we forecast over 17,000 objects may be discovered and characterized in Data Preview 2. We predict that several hundred known objects and thousands of as-of-yet undiscovered UCDs may be detected in Data Preview 2 fields.
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All authors Easton J. Honaker, John E. Gizis, Christian Aganze, Siddharth Chaini, Federica B. Bianco, Maruša Žerjal, Eduardo L. Martín, Riley W. Clarke, Ashton Southwick, Harrison Petrie, Tyler Blask
Earth and Planetary Astrophysics
Planetesimal-Driven Instabilities in Resonant Chains of Cold Neptunes and Their Dynamical Outcomes
Ryan LoRusso, Cristobal Petrovich and Hareesh Gautham Bhaskar
Cold Neptunes and sub-Neptunes are among the most common products of
planet formation and likely dominate the angular-momentum budgets in most planetary systems, yet their dynamical impact on planetary architectures remains poorly understood. Using N-body simulations, we investigate the
evolution of multi-Neptune systems assembled into resonant chains during the gas-disk phase and later coupled to remnant planetesimal disks. We show that planetesimal disks containing $\simeq 1$-$4\%$ of the planetary mass efficiently disrupt resonant chains and trigger global dynamical instabilities on timescales of $1~\mathrm{Myr}$-$1~\mathrm{Gyr}$, providing a pathway for delayed instability long after gas-disk dispersal, albeit with instability timescales that are highly sensitive to disk mass. The ensuing instability drives large-scale orbital rearrangement and loss of
planets through collisions,
tidal disruption, and ejections. Notably, in most systems at least one
planet is scattered inward to $\sim 0.1~\mathrm{au}$ on $\sim 10$-$100$ Myr timescales (for $\sim 5$-$50\; M_\oplus$
planets) following instability onset, with a substantial fraction undergoing
tidal capture or disruption. This
tidal capture can provide a natural pathway to hot Neptune formation, while compact inner chains, if present, would be destroyed on $\sim 100~\mathrm{Myr}$ timescales by cold sub-Neptunes, naturally explaining the observed decline in the resonant fraction. We argue that the predictions of our model, which yields mass-segregated
planets and corresponding relative abundances of cold, wide-orbit, and free-floating
planets, can be tested by ongoing and upcoming microlensing surveys.
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Earth and Planetary Astrophysics
What you see is not necessarily what you get: Interpreting near-infrared scattering phase functions of debris discs
Quincy Bosschaart and Johan Olofsson
Scattering phase functions (SPFs) derived from resolved scattered-light images of debris discs are widely used to infer
dust grain properties, often via parametric forms such as the Henyey-Greenstein (HG) phase function. However, it remains unclear to what extent the inferred scattering behaviour reflects intrinsic
dust properties rather than projection effects, disc geometry, or methodological choices. We test how reliably SPFs and HG asymmetry parameters can be recovered from scattered-light images and identify regimes where
geometric and observational effects introduce significant biases. We use a physically motivated forward-modelling framework combining
dust-scattering calculations, grain dynamics, and ray-tracing to generate synthetic total-intensity images. Since the intrinsic SPFs are known a priori, phase functions extracted from the images can be directly compared to the input scattering behaviour. We explore a grid of grain size distributions, disc inclinations, and opening angles, and fit two-component HG functions to evaluate how well the forward-scattering parameter $g_{1}$ traces grain properties. Even under idealised conditions with perfect knowledge of disc geometry, the recovered phase functions can differ substantially from the intrinsic SPFs. Limited scattering-angle coverage is the dominant effect: strong forward-scattering peaks at small angles are typically unobservable, leading to non-monotonic trends of apparent anisotropy with grain size. Projection effects, line-of-sight mixing, and SPF-extraction choices further modify the recovered phase functions, causing the fitted $g_{1}$ to depend strongly on viewing geometry and methodology. We conclude that SPFs and HG parameters derived from scattered-light images should be interpreted as effective, observation-dependent quantities rather than direct proxies for
dust properties.
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High Energy Astrophysical Phenomena
The impact of plasma instability cooling on intergalactic magnetic field constraints in GeV cascades for optimized instability cooling parameters
Suman Dey, Simone Rossoni and Günter Sigl
Electromagnetic cascades are initiated by TeV gamma rays propagating through the intergalactic medium (IGM), and they can be used to constrain the weak intergalactic
magnetic field (IGMF) in
cosmic voids. Primary TeV
photons produce electrons and positrons through electromagnetic pair production, which can be deflected out of the line-of-sight to the observer by IGMF. In addition, electron-positron pairs can perturb the IGM, triggering
plasma instabilities that can cool down the pairs before they upscatter
cosmic background
photons to GeV energies via inverse Compton (IC) scattering. In this work, we investigate the influence of
plasma instabilities on the cascade spectrum by introducing a parameterized instability model within the publicly available Monte Carlo framework CRPropa 3.2 in the presence of IGMF. We first determine the instability parameters that best reproduce the
Fermi-LAT observations in the absence of any IGMF. We then use extended-emission observations within the observer's field of view, including the effects of the IGMF, to constrain the IGMF strength in the presence of the corresponding best-fit instability-cooling parameters, based on the
Fermi-LAT spectral observations of the blazar 1ES 0229+200. We find that
plasma instabilities with a characteristic length scale of $120$ kpc and a spectral index of $\alpha=-0.5$ are consistent with the observed
photon spectra. We also find that the fit of the observed data is improved by the presence of an IGMF: we obtain an IGMF lower limit of $B \gtrsim 2.7 \times 10^{-17}$ G for an observer field of view $1.0^\circ$.
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High Energy Astrophysical Phenomena
Reginald Christian Bernardo
Langevin
stochastic differential equations provide a dynamical description of
pulsar timing noise and gravitational wave background (GWB) signals. They are also central to state space
algorithms that have gained traction in
pulsar timing array analysis due to their linear computational scaling with the number of observations. In this work, we utilize established methods in
diffusion theory to derive analytical time-domain solutions (means, covariances, and probability density functions) to Langevin equations relevant to red noise and the GWB signal in
pulsars. The solutions give direct physical insight on the dynamics of
pulsar timing signals. As a canonical example, we show that the
pulsar spin frequency modeled as an Ornstein-Uhlenbeck process is mathematically inconsistent with a stationary GWB signal when the timing residual is the direct observable. The nonstationarity can be partially dealt with by marginalizing over long time deterministic trends in the data. Then, we show that a random process based on an overdamped harmonic oscillator supports both a stationary
spin frequency and phase residuals, consistent with a stationary GWB signal. We also turn our
attention to a phenomenological model of a
neutron star – a two-component model with
spin wandering – that has been motivated to explain observed timing noise in
radio pulsars. We derive analytical expressions for the means, covariances, and cross-covariances of the crust and superfluid rotational states driven by white noise. The associated constant deterministic torques are linked to the quadratic
spin-down of
pulsars. The solutions reveal the physical origin of nonstationarity in the residual model: the coexistence of damped and diffusive eigenmodes of the system.
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Astrophysics of Galaxies
3D kinematics of SMC star clusters: residual velocities disentangle kinematically perturbed clusters
Denis M.F. Illesca, Andrés E. Piatti, Matías Chiarpotti et al. (+1 more)
Understanding the kinematic behaviour of the Small Magellanic Cloud (SMC) remains a challenge addressed by many authors using diverse approaches. Over time, increasing observational evidence has accumulated for
tidal perturbations induced by the Large Magellanic Cloud (LMC) on the SMC, especially in its outer regions. In this study, we adopt
star clusters as kinematic tracers of the SMC. We analyse 36 clusters distributed across the
galaxy's structural regions (Northern Bridge, Southern Bridge, Wing/Bridge, West
Halo, Main Body and Counter-Bridge). From each cluster's proper motions, radial velocity and heliocentric distance we estimate Cartesian velocities \((V_x,\,V_y,\,V_z)\) in the SMC reference frame. We also compute the same velocity components under the assumption that the SMC behaves as a rotating disc. We then define the residual velocity \(\Delta V\) for each cluster as the difference between the two velocities derived. Additionally, we perform a kinematic anisotropy analysis to characterise the distribution of kinetic energy across the SMC. We find that increasing values of \(\Delta V\) correlate with increasing cluster distance from the SMC center, and that \(\Delta V \approx 60\ \mathrm{km\,s^{-1}}\) it appears to be a lower limit that separates, in kinematic terms, the areas of
tidal origin from those with the best behavior.
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All authors Denis M.F. Illesca, Andrés E. Piatti, Matías Chiarpotti, Roberto Butrón
Cosmology and Nongalactic Astrophysics
A Dynamical Equilibrium Linking Nanohertz Stochastic Gravitational Wave Background to Cosmic Structure Formation
Manjia Liang, Peng Xu, Ruijun Shi et al. (+6 more)
The
stochastic gravitational wave background (SGWB) is conventionally treated as a passive relic of its astrophysical and cosmological sources, with negligible back-reaction on the matter content of the Universe. Here we show that this assumption needs to be modified once the SGWB and matter are treated as a dynamically coupled non-
equilibrium system. Combining linearized general relativity with the fluctuation-dissipation
theorem, we derive a generalized Langevin framework that drives the coupled system toward a dynamical
equilibrium, which is characterized by a distinctive strain spectrum with a high-frequency cutoff $\mathcal{W}$, and a scale-dependent coupling parameter that screens
gravity progressively for the most massive structures. Three findings support this framework. Fitting the
equilibrium spectrum to the NANOGrav 15-year
dataset yields a Bayes factor of $48\pm 3.8$ over the supermassive black hole binary baseline, achieved entirely within general relativity and the Standard Model. The PTA-calibrated screening mass scale $m_{c}\sim 10^{12}\text{--}10^{14}\,M_{\odot}$ overlaps, with no free cosmological parameter, the $\Lambda$CDM-derived linear-to-nonlinear transition mass $M_{\rm NL}$ of
cosmic structure at $\sim 8\,h^{-1}\,\mathrm{Mpc}$. Most strikingly, promoting this concordance to a structural identification expresses $\mathcal{W}$ entirely in terms of $M_{\rm NL}$, and its inverse acquires a transparent physical reading as a coherence threshold for SGWB-matter coupling. $\mathcal{W}$ is thereby a derived quantity linking nanohertz gravitational-wave observables to the late-time cosmological sector. The framework makes distinctive scale-dependent predictions testable by forthcoming large-scale structure surveys and space-borne gravitational-wave observatories.
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All authors Manjia Liang, Peng Xu, Ruijun Shi, Zhoujian Cao, Ziren Luo, Minghui Du, Qiong Deng, Bo Liang, Jiaxiang Liang
Cosmology and Nongalactic Astrophysics
The peculiar velocity correlation function of the Cosmicflows-4 catalog
Yuyu Wang, Hume A. Feldman, Richard Watkins et al. (+1 more)
We present an analysis of the parallel peculiar velocity correlation function using data from the Cosmicflows-4 (CF4) survey. CF4 significantly extends the depth of the peculiar velocity measurements, mitigating the impact of observers on the
cosmic variance. We examine the distribution of
cosmic variance using different velocity correlation
estimators. The combination of the large peculiar velocity uncertainties and the anisotropy distribution of the CF4 data across the northern and southern hemispheres results in substantial statistical uncertainties in the velocity correlation function. To address this, we test different weighing schemes in the velocity correlation function and implement a more accurate peculiar velocity
estimator that reduces velocity uncertainties, consequently decreasing the statistical uncertainty. Using the CF4 group
dataset, we derive a growth rate of $f\sigma_8=0.384^{+0.116}_{-0.194}$ and a local growth rate of $f\sigma_8=0.569^{+0.054}_{-0.06}$ through a Markov Chain Monte Carlo method.
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All authors Yuyu Wang, Hume A. Feldman, Richard Watkins, Xiaohu Yang
High Energy Astrophysical Phenomena · Cross-listed from nucl-th
Relativistic mean-field models of neutron-rich matter
J. Piekarewicz
The aim of this chapter, focused on relativistic mean-field models and part of the Encyclopedia of
Nuclear Physics, is to provide an introductory, self-contained discussion accessible to a broad audience, including advanced undergraduate students. The chapter surveys the fundamental ideas, assumptions, and theoretical framework underlying relativistic mean-field models, and illustrates their wide range of applications across
nuclear science. Particular emphasis is placed on the central role that these models play in the construction of equations of state for strongly interacting matter, as well as on the intimate connections between
nuclear experiments, astrophysical observations, and theoretical modeling. In this context, relativistic mean-field theory is shown to provide a unified description of bulk
nuclear properties and dense
neutron-rich matter, enabling the interpretation of the remarkable structural and observational properties of
neutron stars in the emerging era of multi-messenger astronomy.
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Astrophysics of Galaxies
Chemistry and ro-vibrational excitation of CH$^+$ in the planetary nebula NGC 7027
Milan Sil, Alexandre Faure, Helmut Wiesemeyer et al. (+5 more)
Small carbon hydride cations, such as the methylidyne ion (CH$^+$), play an important role in the chemistry of the interstellar medium (ISM). They participate in gas-phase reaction networks leading to the formation of hydrocarbon species that act as precursors to more complex organic molecules. CH$^+$ is a highly reactive ion that is rapidly destroyed by H, H$_2$, and free electrons, making its excitation challenging to model. Its level populations depend not only on radiative and inelastic processes but also on chemical formation and destruction rates, a mechanism known as chemical pumping. We investigate this effect using a new set of ab initio state-resolved ro-vibrational (reactive and inelastic) collision data to model the observed CH$^+$ emission. Multiple rotational and ro-vibrational transitions of CH$^+$ detected toward the planetary nebula NGC 7027 are analyzed. The chemical structure of CH$^+$ is modeled with the CLOUDY code using updated reaction rates, providing the temperature and density structure across the nebula. A non-local thermodynamic
equilibrium (NLTE) analysis is performed using CLOUDY and the single-zone RADEX code with a comprehensive set of spectroscopic and collisional data. In addition, chemical formation and destruction processes are implemented in RADEX and explored via Markov Chain Monte Carlo sampling. The CLOUDY model reproduces the observed CH$^+$ line fluxes within a factor of 1.3 on average. It indicates that rotational and ro-vibrational lines arise from physically distinct regions, primarily differing in temperature. RADEX models show that chemical pumping significantly enhances populations above ($\upsilon = 0, J = 1$), strongly increasing ro-vibrational emission, especially in the $\upsilon =2 \to 1$ band. Single-zone models remain limited, highlighting the need for full 1D modeling including all excitation processes.
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All authors Milan Sil, Alexandre Faure, Helmut Wiesemeyer, Pierre Hily-Blant, Tomás González-Lezana, Josh Forer, Jérôme Loreau, François Lique
High Energy Astrophysical Phenomena
The Stack Search Tests on FAST Data: Discovery of Six Faint Isolated Millisecond Pulsars in NGC 6517 and NGC 7078 (M15)
Yinfeng Dai, Xing-Jiang Zhu, Zhichen Pan et al. (+16 more)
We report the discovery of six faint millisecond
pulsars (MSPs) in the globular clusters NGC 6517 and NGC 7078 (M15) using the Five-hundred-meter Aperture Spherical
radio Telescope (FAST). These discoveries were enabled by stacking power spectra from multiple observations, a method that effectively boosts the signal-to-noise ratio of faint sources. In NGC 6517, we identified four new MSPs (NGC 6517S-V) with
spin periods ranging from 3.68 to 6.02 ms and dispersion measures (DMs) between 182.45 and 182.85 pc cm^-3. In M15, two additional MSPs (M15M and M15N) were discovered, with
spin periods of 4.83 and 9.28 ms, and DMs of 67.89 and 66.65 pc cm^-3, respectively. A phase-coherent timing solution has been obtained for M15M; however, sparse detection rates currently preclude phase-connected solutions for the remaining five
pulsars. Current timing parameters suggest all six MSPs are isolated, which is consistent with the expected
pulsar populations in core-collapsed globular clusters. Notably,
pulsars M15N, NGC 6517U, and NGC 6517V eluded detection by standard frequency-domain searches (e.g., PRESTO-based) and the Fast Folding
Algorithm, demonstrating that the stack search technique significantly enhances detection sensitivity to inherently faint
pulsar signals.
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All authors Yinfeng Dai, Xing-Jiang Zhu, Zhichen Pan, Lei Qian, Li-yun Zhang, Dejiang Yin, Yu Pan, Bo Peng, Baoda Li, Yujie Lian, Yaowei Li, Yuxiao Wu, Menglin Huang, Qiaoli Hao, Xingyi Wang, Xianghua Niu, Jinyou Song, Minglei Guo, Shuangyuan Chen
Earth and Planetary Astrophysics
Substructure in externally irradiated protoplanetary disks, I. spirals and rings in two-dimensional radiation hydrodynamics
Alexandros Ziampras, Lin Qiao and Thomas J. Haworth
It is known that the external irradiation of protoplanetary disks by nearby massive
stars can result in mass loss that impacts the disk
evolution, however the dynamical impact of external irradiation upon the disk itself has not been explored in detail. We aim to investigate the dynamical effect of asymmetric external irradiation on the structure of such disks. We perform two-dimensional multi-fluid radiation hydrodynamical simulations of protoplanetary disks subject to external irradiation using the PLUTO code, with external irradiation modeled as a plane-parallel flux and a simplified nonaxisymmetric heating rate corresponding to the thermal reemission from hot material within the region marginally optically thick to the external irradiation. We find that a nearby massive
star can, under certain conditions, induce significant dynamical effects on a protoplanetary disk, including a shadowed region, pronounced spiral arms in gas, and rings and gaps in
dust. The dynamics are caused by the temperature asymmetry driven and maintained by external irradiation, akin to the well-established mechanism of shadow-induced spirals and rings in disk with shadowing from their inner regions. Our results show that if an external temperature asymmetry can be induced it can have a significant dynamical impact on the disk itself (in addition to the well-studied mass loss and truncation effects due to external irradiation), possibly even driving substructure. This
prompts further investigation with detailed, dynamical radiative transfer models.
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Astrophysics of Galaxies
Extended coronal line emission and new clues to a possible dual AGN in the merger J1356+1026
M. Bianchin, C. Ramos Almeida, O. González-Martín et al. (+12 more)
Merging luminous
galaxies are ideal laboratories to study some of the most extreme astrophysical phenomena. The local (z=0.1232) obscured
quasar J1356+1026 has two
nuclei, North and South (J1356N and J1356S), but despite numerous efforts, J1356S had not yet been confirmed as an AGN. Thanks to the superb sensitivity and spatial resolution of the MIRI/MRS instrument on board the JWST, we present new evidence suggesting that J1356S may indeed host an AGN with log L$_{\rm bol}=43.4\pm^{0.6}_{0.5} erg s^{-1}$. This is supported by the detection of strong coronal line emission at this location and by a spectral shape that differs from that of J1356N and those of the narrow-line region (NLR). Aided by the spatially resolved information of MIRI/MRS and VLT/SINFONI, we also find that the high ionization gas, traced by the coronal lines [Ne V]$14.3~\mu$m and [Si VI]$1.963 \mu$m, has an extension of ~13-15.5 kpc. This is likely a lower limit of the true extension, as suggested by the comparison with optical imaging from HST. {The extended [Ne V] emission can be accounted for by photoionization from the
quasar in J1356N in a relatively low density environment, ranging from $\rm n_e\leq 2000-3800 cm^{-3}$ in J1356N and $\rm n_e\leq 600-1200 cm^{-3}$ in J1356S and the NLR, as measured from the [Ne V]$14.3\mu$m and $24.3~\mu$m lines.
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All authors M. Bianchin, C. Ramos Almeida, O. González-Martín, M. V. Zanchettin, M. Carneiro, M. Pereira-Santaella, C. Tadhunter, G. Speranza, I. García-Bernete, A. Audibert, A. Alonso-Herrero, D. Rigopoulou, A. Labiano, J. A. Acosta-Pulido, S. García-Burillo
Instrumentation and Methods for Astrophysics
A Statistical-AI Framework for Detecting Transient Flares in SDSS Stripe 82 Quasar Light Curves
Atal Agrawal
Quasars exhibit
stochastic variability across wavelengths, typically well described by a Damped Random Walk (DRW). Occasionally, however, they undergo extreme luminosity changes–known as
flares–that represent significant departures from this baseline behavior and provide valuable probes of
accretion disc dynamics and the physics of supermassive black hole fueling. Although modern transient surveys have spurred growing interest in
flare detection, no systematic search has yet been conducted within the legacy SDSS Stripe 82
dataset, which contains 9,258 spectroscopically confirmed
quasars observed over a ~10-year baseline. The principal statistical challenge is distinguishing these rare events from the ever-present
stochastic variability. To address this, we present
FLARE (
Flare detection via physics-informed Learning, Anomaly scoring, and Recognition Engine), a modular three-stage framework for detecting transient
flares in
quasar light curves.
FLARE models baseline DRW behavior, applies statistical anomaly scoring to flag candidate events, and employs a recognition engine to verify detections. For the Stripe 82 implementation, we deploy two complementary baselines–a physics-informed probabilistic Gated Recurrent Unit (GRU) trained on simulated DRW light curves, and an iterative Ornstein-Uhlenbeck (OU) process fitted directly to observed data with outlier masking–followed by Extreme Value Theory (EVT) for anomaly scoring. We
benchmark twelve open-weight and proprietary
Vision Language Models (VLMs) as recognition engines for final candidate verification. Detection is performed on r-band light curves, with candidates cross-checked against g-band data to rule out instrumental artifacts. Applying this framework, we identify 51
quasars exhibiting distinct flaring activity.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Probing Majoron Dark Matter with Gravitational Wave Detectors
Ippei Obata and Tsutomu T. Yanagida
The Majoron is a hypothetical (pseudo) Nambu-Goldstone
boson arising from the spontaneous breaking of a global
lepton number
symmetry, and is known as a candidate for dark matter in our Universe. In this paper, we investigate the possibility of probing the Majoron dark matter with a linear optical cavity used in the interferometric gravitational wave detectors. We consider a scenario in which the Majoron dark matter couples to
photons through a QED anomaly, leading to an oscillatory
photon birefringence induced by the coherent dark matter background. The anomaly coefficient is fixed by requiring the model to simultaneously reproduce the electroweak
Higgs scale and a typical right-handed Majorana
neutrino mass scale, and the resulting dark matter-
photon coupling naturally falls within the sensitivity range of optical interferometers. By incorporating additional optics to extract the birefringence signal, we find that ground-based
laser interferometers such as Advanced LIGO, KAGRA, as well as future detectors, can probe a region of the parameter space of Majoron dark matter.
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Earth and Planetary Astrophysics
The evolution of exocomets and their source populations
Alexander J. Mustill, Tim Pearce, Michele Bannister et al. (+12 more)
We review the current state of knowledge of the long-term
evolution of the small bodies that give rise to comets and exocomets, as well as their reservoirs. The active cometary phase is only transitory, and bodies that become comets pass from a source population, such as the Kuiper Belt, Oort Cloud or their extra-
solar analogues, through the active cometary phase, to eventual dormancy or destruction. We discuss dynamical delivery channels that can move comets from their source reservoirs to orbits with small periapsides, and the depletion of these reservoirs by dynamical and collisional means. We also discuss the physical
evolution of cometary
nuclei, especially in light of recent advances from missions to
Solar System comets such as Rosetta's visit to 67P. We then describe our current knowledge of interstellar objects, which can originate from the same source regions as exocomets but be amenable to detailed study when they enter the
Solar System. We include a summary of
stellar winds emanating from different types of
stars, which become increasingly strong once
stars leave the Main Sequence. This is followed by a description of how small bodies are affected by
stellar evolution, and the range of comet-like phenomena observed towards white
dwarf stars. Overall, while we have an increasingly good picture of the physical and dynamical
evolution of
Solar System comets, a number of large gaps remain in our knowledge of the physics of exocomets, related to our inability to directly probe these bodies and many of the
planets that might be affecting their orbits.
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All authors Alexander J. Mustill, Tim Pearce, Michele Bannister, Susanne Pfalzner, Dag Evensberget, Dimitri Veras, Rosita Kokotanekova, Matthew Hopkins, Dennis Bodewits, Darryl Z. Seligman, Isabel Rebollido, Raphael Marschall, Bin Yang, Klaudia Jaworska, Xabier Pérez Couto
High Energy Astrophysical Phenomena
How many VHE gamma-ray binaries with young pulsars can be observed?
A. M. Bykov, A. G. Kuranov, A. E. Petrov et al. (+1 more)
A population of
Galactic gamma-ray binaries is currently emerging due to ever increasing sensitivity of gamma-ray observatories. The detection of very high energy (VHE)
photons with energies well above 10 TeV from a dozen of sources and the estimated power of those sources make them potentially interesting
cosmic ray accelerators. Multi-wavelength observations of gamma-ray binaries revealed that most of them include a young massive
star in pair with a relativistic companion, either a black hole or energetic
pulsar. Fast
stellar winds interacting with powerful relativistic
outflows from
pulsars or the black hole jets in microquasars are favorable sites for VHE particle acceleration. To estimate the expected number of gamma-ray binaries, we present results of population synthesis calculations of
Galactic binaries in which a young massive OB- or Be-
star is accompanied by a
pulsar capable of producing a powerful relativistic
outflow. The distributions over the binary eccentricities, orbital periods, Be-disk inclinations, and the
pulsar braking energy losses are taken into account. Conditions for a binary to accelerate VHE particles, radiate and absorb the non-thermal
photons that may reach the observer are discussed. We model the anisotropic structure of the zone of interaction of the relativistic
pulsar wind with the strongly magnetized massive
star's wind. The
stellar winds with strong ($\sim$ Gauss)
magnetic fields at $\sim$ AU distances colliding with powerful
pulsar outflows are capable of accelerating particles up to PeV energies at some orbital configurations and phases. The strong
magnetic field in the interaction region produces a highly anisotropic structure of the particle accelerator and emitter in the
pulsar outflow. The anisotropic radiation pattern may affect the gamma-ray
photon absorption and the number of the observed gamma-ray loud systems.
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All authors A. M. Bykov, A. G. Kuranov, A. E. Petrov, K. A. Postnov
Astrophysics of Galaxies
Evangelos D. Paspaliaris, Simone Bianchi, Edvige Corbelli et al. (+8 more)
DustPedia and LVL are two samples representative of the local
galaxy population, including in total 1011 unique objects of all morphological types, with a wide range of
stellar masses ($M_*$) and
star-formation activity, and a spectral coverage from the FUV to the FIR. The purpose of this work is to show that these samples cover two complementary ranges in $M_*$ and morphology, making them an ideal set for constraining the dominant processes in the
evolution of the
galactic dust content. Using the multiwavelength data provided by the two surveys, we fitted the
galaxies' spectral energy distribution and estimated their physical properties, in particular the $M_*$, $sM_\mathrm{dust}=M_\mathrm{dust}/M_*$, and sSFR = SFR$/M_*$. By combining DustPedia and LVL, we highlight that the $\log_{10}(sM_{\rm dust})$-$\log_{10}(M_*)$ trend is not monotonic. Thanks to a large number of objects across a wide range of $M_*$, we have been able to fit two smoothly-joined linear correlations: a positive for $\log_{10}(M_{*}/$M$_\odot)\lesssim9.5$ (mainly LVL late spirals and irregulars), and a negative one for larger-mass, mainly DustPedia spirals (early types are distinct and more dispersed in the same mass regime). For $\log_{10}(M_{*}/$M$_\odot)>9.5$, we confirm a strong sM_
dust-sSFR correlation;
dwarf galaxies, instead, lie below this trend, with a large scatter of $sM_{\rm dust}$, for -10.5<$\log_{10}$(sSFR/yr$^{-1}$)<-9.0. By using chemical
evolution models we find that the observed $\log_{10}(sM_{\rm dust})$-$\log_{10}(M_{*})$ and $\log_{10}(sM_{\rm dust})$-$\log_{10}$(sSFR) trends can be interpreted mainly by variations in the initial gas mass budget and the
galaxy ages, respectively. Low-mass Sm-Irr
galaxies with low $sM_{\rm dust}$ and high sSFR can only be reproduced by the models by assuming high photofragmentation rate of large grains, and/or low grain-growth in clouds.
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All authors Evangelos D. Paspaliaris, Simone Bianchi, Edvige Corbelli, Angelos Nersesian, Frédéric Galliano, Viviana Casasola, Francesco Calura, Emmanuel M. Xilouris, Francesca Pozzi, Georgios Magdis, Vidhi Tailor
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
Caustic formation in DBI models: Wave propagation on planar domain walls
E. Babichev, B. Gafarov, S. Ramazanov et al. (+1 more)
We investigate propagation of generic waves on thin planar domain walls effectively described by the scalar Dirac-Born-Infeld model (DBI). We pay a particular
attention to the possibility of caustic formation - the process, which may lead to intensive particle emission by domain walls. It is demonstrated that no singularities arise in DBI in 2D flat spacetime in the
hyperbolic case, if one starts from smooth initial conditions. Technically, this happens because the same family characteristics of the relevant partial differential equation remain parallel at all the times, albeit not being straight lines generically. Crucially, characteristic curves cease to be parallel beyond the simplified setup of DBI in 2D flat spacetime. In particular, this is shown to be the case in $D>2$ for spherical waves, in an expanding Universe, and in the case of a minimal deformation of DBI necessary for avoiding the domain wall problem in cosmology. However, we prove that DBI remains caustic free in the
hyperbolic case in all these physically relevant situations. This strongly suggests that caustics can form on planar domain walls only due to the loss of hyperbolicity, and they have a cusp profile. We demonstrate, how the non-trivial structure of DBI characteristics beyond the 2D flat spacetime setup uncovered in this work can significantly affect cusp formation.
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All authors E. Babichev, B. Gafarov, S. Ramazanov, M. Valencia-Villegas
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Detecting Chiral Gravitational Wave Background with a Dipole Pulsar Timing Array
Baoyu Xu, Hanyu Jiang, Rong-Gen Cai et al. (+2 more)
The
pulsar timing array (PTA) is a powerful technique for detecting nanohertz gravitational wave backgrounds (GWBs). However, conventional PTAs lack sensitivity to parity violation in the GWB. In this work, we propose a dipole
pulsar timing array system (dPTA). By deriving the overlap reduction functions (ORFs) from the cross-correlation of timing signals, we find that this system exhibits sensitivity to
chiral GWBs in the nanohertz regime. Furthermore, through numerical calculations of its sensitivity curves, we demonstrate that the dPTA extends the detectable frequency range of PTAs for GWBs from the nanohertz to the microhertz regime.
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All authors Baoyu Xu, Hanyu Jiang, Rong-Gen Cai, Misao Sasaki, Yun-Long Zhang
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Observational Quantities in Quasi-Newtonian Descriptions of Cosmological Space-Times
Asta Heinesen, Davide Fontana and Timothy Clifton
We investigate measures of distance and
redshift in cosmological space-times that admit a shear-free foliation, which we henceforth refer to as `quasi-Newtonian'. Space expands isotropically in this description, and small-scale gravitational physics has a natural Newtonian limit, which makes it ideal for considering the physics of wide classes of cosmological models. By assuming that the energy-momentum tensor is dominated by rest-mass density, and that the 3-velocity of matter is small in the quasi-Newtonian frame, we derive fundamental results for kinematics and light propagation. Our results provide a new way of formulating general-relativistic cosmologies with non-perturbative structures in terms of quantities that can be understood from cosmological perturbation theory and post-Newtonian expansions, and allow us to quantify departures of observables from the predictions of Friedmann cosmology. It thereby provides a route to understanding inherently relativistic space-time structures, such as those that occur in Lemaître-Tolman-Bondi, Szekeres solutions, and Bianchi cosmologies in terms of Newtonian degrees of freedom. We illustrate our results using the degenerate Kasner solution as an example, and explain how our approach can be used to provide new insights into the current cosmological tensions.
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Earth and Planetary Astrophysics
In-flight calibration of ESA Hera's HyperScout-H imager
G. P. Prodan, M. Popescu, J. de León et al. (+21 more)
ESA's Hera space mission is on its way to the mission target, the binary asteroid (65803) Didymos. HyperScout-H, one of the instruments onboard Hera, is a hyperspectral imager operating in the visible and near-infrared regions between 0.65 and 0.95 microns. HyperScout-H will enable a detailed assessment of the composition of both objects, Didymos and its satellite Dimorphos, the characterization of space weathering effects, and the possible presence of exogenous material on their surfaces. To monitor instrument functionality, calibration exposures are acquired regularly. This article describes the in-flight calibrations carried out for HyperScout-H during the commissioning and cruise phases. Bias and dark exposures, as well as
stellar field observations, were acquired several times after launch. We update the calibration data and monitor instrument performance in the space environment. In five images, the surface of Mars fills the entire field of view, enabling cross-validation of HyperScout-H results with those reported by other Mars missions. The calibration data indicate that the bias pattern is stable, the dark current remains negligible for short exposures, and the detector response is highly linear. We quantify the field-of-view
alignment and
geometric distortion, and evaluate the point spread function based on the
stellar field observations.
Stellar observations and Mars swing-by data provide updated radiometric calibration constants, suggesting that in-flight conditions have slightly modified the detector's spectral response. In-flight calibrations are essential to ensure data quality and reliability. The results obtained for HyperScout-H demonstrate that the instrument can achieve its scientific goals in observations of the Didymos-Dimorphos system.
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All authors G. P. Prodan, M. Popescu, J. de León, G. Kovács, M. Küppers, B. Grieger, C. Guerbuez, E. Tatsumi, J. Licandro, A. Escalante López, V. Nagy, A. Farina, B. A. Dumitru, G. Poggiali, J. B. Vincent, T. Kohout, I. Petrisor, E. Palomba, M. Esposito, N. Vercruyssen, S. Sugita, M. Lazzarin, P. Abell, P. Michel
High Energy Astrophysical Phenomena
Flux variability of the "10 keV feature" of 4U 0115+63
Katrin Berger, Ekaterina Sokolova-Lapa, Ralf Ballhausen et al. (+14 more)
X-ray spectra of
accretion-powered X-ray
pulsars can often be described using a power-law continuum with a high-energy cutoff, which might be further modified by additional spectral components. The Be X-ray binary system 4U 0115+63 is well known for having one of the highest numbers of detected harmonics of its cyclotron resonant scattering features (CRSFs), a pronounced spectral component known as the ”10 keV feature,” and quasiperiodic oscillations (QPOs) with a period of about 500 s during outbursts. The changes in count rate by a factor of two during the approximately 500 s QPOs allow us to probe the variation in the spectral components with flux. We study the ”10 keV feature” in emission, aiming to disentangle it from the broadband continuum and CRSFs and investigate its origin. We focus on the flux-dependent behavior of the CRSF and its harmonics, and particularly the contribution of the ”10 keV feature,” as seen in the flux-resolved analysis of two NuSTAR observations of the 2015 outburst. Comparing the flux-resolved spectra of a given observation with the respective total
dataset revealed a distinct change in overall spectral shape at the position of the ”10 keV feature” but no comparable deviation at the energies of the harmonic CRSFs. The change associated with the ”10 keV feature” does not seem to involve its centroid energy, which remains constant within a given observation. We find indications for an anticorrelation between the continuum flux and the ratio of the ”10 keV feature” flux to the continuum flux within each observation. The analysis strengthens previous claims that the ”10 keV feature” shows some independence from the remaining features. This result supports the interpretation that the ”10 keV feature” has a different formation mechanism than the continuum emission, although its origin lies within the same physical environment.
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All authors Katrin Berger, Ekaterina Sokolova-Lapa, Ralf Ballhausen, Aafia Zainab, Philipp Thalhammer, Nicolas Zalot, Katja Pottschmidt, Carlo Ferrigno, Richard E. Rothschild, Felix Fuerst, Peter Kretschmar, Joel B. Coley, Pragati Pradhan, Brent F. West, Peter A. Becker, Alicia Rouco-Escorial, Joern Wilms
Solar and Stellar Astrophysics
Chromospheric turbulence as a regulator of stellar wind mass flux
Munehito Shoda, Tom Van Doorsselaere and Allan Sacha Brun
The mass flux of
solar and
stellar winds is a key quantity for
stellar evolution and space weather, yet its physical regulation mechanism remains an unsolved problem. In particular, conventional Alfvén wave–driven models that self-consistently connect the
stellar surface to the
stellar wind fail to reproduce the observed scaling between
stellar X-ray flux and mass-loss rate, a discrepancy that can be largely attributed to the dissipation of a substantial fraction of the wave energy by chromospheric
turbulence. To address this issue, we aim to clarify the role of chromospheric
turbulence in regulating the
stellar wind mass flux. We perform one-dimensional wave-driven wind simulations, comparing cases with and without chromospheric
turbulence suppression to assess its impact on coronal and wind properties. We find that suppressing chromospheric
turbulence leads to a systematic increase in the coronal particle flux, and hence the wind mass flux, by up to an order of magnitude, particularly in regions of moderately strong
magnetic field. This behavior arises from a combination of changes in the Poynting flux at the coronal base and in the asymptotic wind speed. Furthermore, the model with chromospheric
turbulence suppression reproduces the observed empirical scaling between coronal
magnetic field strength and mass flux without invoking additional energy input mechanisms such as interchange reconnection. These results identify the chromospheric
turbulence as a key factor in regulating
stellar wind mass flux and highlight the importance of incorporating its effects in models that connect the
stellar surface and the
stellar wind.
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